HR: 1320h
AN: S43A-0975    [Abstracts]
TI: Monitoring non-linear wave propagation in the 2004 Garner Valley demonstration project
AU: * Bodin, P
EM: pbodin@memphis.edu
AF: CERI, U. of Memphis, Memphis, TN 38152
AU: Brackman, T
EM: tbrackmn@memphis.edu
AF: CERI, U. of Memphis, Memphis, TN 38152
AU: Lawrence, Z
EM: zlawrenc@memphis.edu
AF: CERI, U. of Memphis, Memphis, TN 38152
AU: Gomberg, J
EM: gomberg@usgs.gov
AF: US Geological Survey, 3876 Ste. 2, Memphis, TN 38152
AU: Steidl, J
EM: steidl@crustal.ucsb.edu
AF: Institute for Crustal Studies, U.C. Santa Barbara, Santa Barbara, CA 93106
AU: Meng, F
EM: fymenq@mail.utexas.edu
AF: Department of Civil Engineering, U. of Texas at Austin, Austin, TX 78712
AU: Stokoe, K
EM: k.stokoe@mail.utexas.edu
AF: Department of Civil Engineering, U. of Texas at Austin, Austin, TX 78712
AU: Johnson, P
EM: paj@lanl.gov
AF: Nonlinear Elasticity Group, Los Alamos National Lab, Los Alamos, NM 87545
AU: Pearce, F
EM: fpearce@lanl.gov
AF: Nonlinear Elasticity Group, Los Alamos National Lab, Los Alamos, NM 87545
AB: On August 18-19, 2004, we performed a series of prototype experiments near the NEES Garner Valley Digital Array (GVDA) to assess the characteristics of non-linear elastic behavior at a deep soil site. We made several different types of observations designed to quantify modulus reduction associated with non-linear wave propagation. In one, a small-scale (1m station spacing) array of accelerometers recorded strong ground motion, both vertical and horizontal, immediately adjacent to a specially designed vibroseis truck (NEES's "TRex"). In this study we focus on the observations from a related experiment: a small-scale (2m station spacing) multi-channel seismograph array that used a sledgehammer source to estimate wave propagation velocities before and after a period of intense ground shaking. This experiment was designed to test the hypothesis that if strong shaking caused rather long-lived changes in the material properties of the soils at the GDVA site, we would see changes in the propagation velocities of surface waves that traversed the experiment locale. Operational considerations permitted us to make three sets of observations before shaking the site, and only one afterward--about 2 hours after. Our stations were laid out in a "star" pattern with TRex in the center of 4 lines of 6 seismometers each (TRex's vibrator pad is about 2.5 m square). To date we have only examined data from one of the lines. Our preliminary analysis reveals evidence for significant changes in the dispersion of surface waves before and after strong shaking. Seismic velocities 2 hours after strong shaking were on the order of 10% slower than before shaking. The volume of material affected extends at least 6 m from the vibroseis pad. It is unclear at this time how much of the difference in velocities was due to modulus reduction, and how much to compaction-induced density increase. The results will be used to help constrain interpretations of recordings of the strong shaking itself made by the nearby array of accelerometers.
DE: 7200 SEISMOLOGY
DE: 7212 Earthquake ground motions and engineering
SC: Seismology [S]
MN: 2004 AGU Fall Meeting